(C) JWE using AES Key Wrap and AES_128_CBC_HMAC_SHA_256

This example duplicates the example A.3 in RFC 7516 for JSON Web Encryption (JWE).

Note: This example requires Chilkat v9.5.0.66 or greater.

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#include <C_CkJwe.h>
#include <C_CkJsonObject.h>
#include <C_CkStringBuilder.h>

void ChilkatSample(void)
    {
    BOOL success;
    const char *plaintext;
    HCkJwe jwe;
    HCkJsonObject jweProtHdr;
    const char *aesWrappingKey;
    const char *strJwe;
    HCkJwe jwe2;
    const char *originalPlaintext;
    HCkStringBuilder sbJwe;

    // This requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Note: This example requires Chilkat v9.5.0.66 or greater.

    plaintext = "Live long and prosper.";

    jwe = CkJwe_Create();

    // First build the JWE Protected Header: {"alg":"A128KW","enc":"A128CBC-HS256"}
    jweProtHdr = CkJsonObject_Create();
    CkJsonObject_AppendString(jweProtHdr,"alg","A128KW");
    CkJsonObject_AppendString(jweProtHdr,"enc","A128CBC-HS256");
    CkJwe_SetProtectedHeader(jwe,jweProtHdr);

    printf("JWE Protected Header: %s\n",CkJsonObject_emit(jweProtHdr));
    printf("--\n");

    // The example A.3 in RFC 7516 uses the following 128-bit AES key,
    // specified in JWK (JSON Web Key) format:
    //      {"kty":"oct",
    //       "k":"GawgguFyGrWKav7AX4VKUg"
    //      }
    // This is just a way of saying: The key type ("kty") is 
    // a bunch of octets ("k") in base64url encoding.
    // We can simply set the AES wrapping key like this:
    aesWrappingKey = "GawgguFyGrWKav7AX4VKUg";
    CkJwe_SetWrappingKey(jwe,0,aesWrappingKey,"base64url");

    // Encrypt and return the JWE:
    strJwe = CkJwe_encrypt(jwe,plaintext,"utf-8");
    if (CkJwe_getLastMethodSuccess(jwe) != TRUE) {
        printf("%s\n",CkJwe_lastErrorText(jwe));
        CkJwe_Dispose(jwe);
        CkJsonObject_Dispose(jweProtHdr);
        return;
    }

    // Show the JWE we just created:
    printf("%s\n",strJwe);

    // Decrypt the JWE that was just produced.
    // 1) Load the JWE.
    // 2) Set the AES wrapping key.
    // 3) Decrypt.
    jwe2 = CkJwe_Create();
    success = CkJwe_LoadJwe(jwe2,strJwe);
    if (success != TRUE) {
        printf("%s\n",CkJwe_lastErrorText(jwe2));
        CkJwe_Dispose(jwe);
        CkJsonObject_Dispose(jweProtHdr);
        CkJwe_Dispose(jwe2);
        return;
    }

    // Set the AES wrap key.
    CkJwe_SetWrappingKey(jwe2,0,aesWrappingKey,"base64url");

    // Decrypt.
    originalPlaintext = CkJwe_decrypt(jwe2,0,"utf-8");
    if (CkJwe_getLastMethodSuccess(jwe2) != TRUE) {
        printf("%s\n",CkJwe_lastErrorText(jwe2));
        CkJwe_Dispose(jwe);
        CkJsonObject_Dispose(jweProtHdr);
        CkJwe_Dispose(jwe2);
        return;
    }

    printf("original text: \n");
    printf("%s\n",originalPlaintext);

    // ---------------------------------------------------------------------------------
    // It should also be possible to decrypt the JWE as shown in RFC 7516, Appendix A.3.7
    // because it was produced using the same AES Wrap key.

    sbJwe = CkStringBuilder_Create();
    CkStringBuilder_Append(sbJwe,"eyJhbGciOiJBMTI4S1ciLCJlbmMiOiJBMTI4Q0JDLUhTMjU2In0.");
    CkStringBuilder_Append(sbJwe,"6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ.");
    CkStringBuilder_Append(sbJwe,"AxY8DCtDaGlsbGljb3RoZQ.");
    CkStringBuilder_Append(sbJwe,"KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY.");
    CkStringBuilder_Append(sbJwe,"U0m_YmjN04DJvceFICbCVQ");

    success = CkJwe_LoadJweSb(jwe2,sbJwe);
    if (success != TRUE) {
        printf("%s\n",CkJwe_lastErrorText(jwe2));
        CkJwe_Dispose(jwe);
        CkJsonObject_Dispose(jweProtHdr);
        CkJwe_Dispose(jwe2);
        CkStringBuilder_Dispose(sbJwe);
        return;
    }

    CkJwe_SetWrappingKey(jwe2,0,aesWrappingKey,"base64url");

    // Decrypt.
    originalPlaintext = CkJwe_decrypt(jwe2,0,"utf-8");
    if (CkJwe_getLastMethodSuccess(jwe2) != TRUE) {
        printf("%s\n",CkJwe_lastErrorText(jwe2));
        CkJwe_Dispose(jwe);
        CkJsonObject_Dispose(jweProtHdr);
        CkJwe_Dispose(jwe2);
        CkStringBuilder_Dispose(sbJwe);
        return;
    }

    printf("%s\n",originalPlaintext);


    CkJwe_Dispose(jwe);
    CkJsonObject_Dispose(jweProtHdr);
    CkJwe_Dispose(jwe2);
    CkStringBuilder_Dispose(sbJwe);

    }